----- Original Message -----
> From: gre...@linuxfoundation.org
> To: "jani nikula" <jani.nik...@intel.com>, b...@hackerdom.ru,
> b...@bwidawsk.net, ch...@chris-wilson.co.uk, "daniel
> vetter" <daniel.vet...@ffwll.ch>
> Cc: stable@vger.kernel.org
> Sent: Wednesday, January 23, 2013 9:16:52 AM
> Subject: FAILED: patch "[PATCH] drm/i915: fix FORCEWAKE posting reads" failed
> to apply to 3.7-stable tree
>
>
> The patch below does not apply to the 3.7-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git
> commit
> id to <stable@vger.kernel.org>.
FYI, I have just back-ported this in a new thread.
>
> thanks,
>
> greg k-h
>
> ------------------ original commit in Linus's tree ------------------
>
> From b514407547890686572606c9dfa4b7f832db9958 Mon Sep 17 00:00:00
> 2001
> From: Jani Nikula <jani.nik...@intel.com>
> Date: Thu, 17 Jan 2013 10:24:09 +0200
> Subject: [PATCH] drm/i915: fix FORCEWAKE posting reads
>
> We stopped reading FORCEWAKE for posting reads in
>
> commit 8dee3eea3ccd3b6c00a8d3a08dd715d6adf737dd
> Author: Ben Widawsky <b...@bwidawsk.net>
> Date: Sat Sep 1 22:59:50 2012 -0700
>
> drm/i915: Never read FORCEWAKE
>
> and started using something from the same cacheline instead. On the
> bug reporter's machine this broke entering rc6 states after a
> suspend/resume cycle. It turns out reading ECOBUS as posting read
> worked fine, while GTFIFODBG did not, preventing RC6 states after
> suspend/resume per the bug report referenced below. It's not entirely
> clear why, but clearly GTFIFODBG was nowhere near the same cacheline
> or address range as FORCEWAKE.
>
> Trying out various registers for posting reads showed that all tested
> registers for which NEEDS_FORCE_WAKE() (in i915_drv.c) returns true
> work. Conversely, most (but not quite all) registers for which
> NEEDS_FORCE_WAKE() returns false do not work. Details in the
> referenced
> bug.
>
> Based on the above, add posting reads on ECOBUS where GTFIFODBG was
> previously relied on.
>
> In true cargo cult spirit, add posting reads for FORCEWAKE_VLV writes
> as
> well, but instead of ECOBUS, use FORCEWAKE_ACK_VLV which is in the
> same
> address range as FORCEWAKE_VLV.
>
> v2: Add more details to the commit message. No functional changes.
>
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=52411
> Reported-and-tested-by: Alexander Bersenev <b...@hackerdom.ru>
> CC: Ben Widawsky <b...@bwidawsk.net>
> Signed-off-by: Jani Nikula <jani.nik...@intel.com>
> Reviewed-by: Chris Wilson <ch...@chris-wilson.co.uk>
> Cc: stable@vger.kernel.org
> [danvet: add cc: stable and make the commit message a bit clearer
> that
> this is a regression fix and what exactly broke.]
> Signed-off-by: Daniel Vetter <daniel.vet...@ffwll.ch>
>
> diff --git a/drivers/gpu/drm/i915/intel_pm.c
> b/drivers/gpu/drm/i915/intel_pm.c
> index e83a117..3280cff 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -4250,7 +4250,8 @@ static void __gen6_gt_force_wake_get(struct
> drm_i915_private *dev_priv)
> static void __gen6_gt_force_wake_mt_reset(struct drm_i915_private
> *dev_priv)
> {
> I915_WRITE_NOTRACE(FORCEWAKE_MT, _MASKED_BIT_DISABLE(0xffff));
> - POSTING_READ(ECOBUS); /* something from same cacheline, but
> !FORCEWAKE */
> + /* something from same cacheline, but !FORCEWAKE_MT */
> + POSTING_READ(ECOBUS);
> }
>
> static void __gen6_gt_force_wake_mt_get(struct drm_i915_private
> *dev_priv)
> @@ -4267,7 +4268,8 @@ static void __gen6_gt_force_wake_mt_get(struct
> drm_i915_private *dev_priv)
> DRM_ERROR("Timed out waiting for forcewake old ack to
> clear.\n");
>
> I915_WRITE_NOTRACE(FORCEWAKE_MT,
> _MASKED_BIT_ENABLE(FORCEWAKE_KERNEL));
> - POSTING_READ(ECOBUS); /* something from same cacheline, but
> !FORCEWAKE */
> + /* something from same cacheline, but !FORCEWAKE_MT */
> + POSTING_READ(ECOBUS);
>
> if (wait_for_atomic((I915_READ_NOTRACE(forcewake_ack) & 1),
> FORCEWAKE_ACK_TIMEOUT_MS))
> @@ -4304,14 +4306,16 @@ void gen6_gt_check_fifodbg(struct
> drm_i915_private *dev_priv)
> static void __gen6_gt_force_wake_put(struct drm_i915_private
> *dev_priv)
> {
> I915_WRITE_NOTRACE(FORCEWAKE, 0);
> - /* gen6_gt_check_fifodbg doubles as the POSTING_READ */
> + /* something from same cacheline, but !FORCEWAKE */
> + POSTING_READ(ECOBUS);
> gen6_gt_check_fifodbg(dev_priv);
> }
>
> static void __gen6_gt_force_wake_mt_put(struct drm_i915_private
> *dev_priv)
> {
> I915_WRITE_NOTRACE(FORCEWAKE_MT,
> _MASKED_BIT_DISABLE(FORCEWAKE_KERNEL));
> - /* gen6_gt_check_fifodbg doubles as the POSTING_READ */
> + /* something from same cacheline, but !FORCEWAKE_MT */
> + POSTING_READ(ECOBUS);
> gen6_gt_check_fifodbg(dev_priv);
> }
>
> @@ -4351,6 +4355,8 @@ int __gen6_gt_wait_for_fifo(struct
> drm_i915_private *dev_priv)
> static void vlv_force_wake_reset(struct drm_i915_private *dev_priv)
> {
> I915_WRITE_NOTRACE(FORCEWAKE_VLV, _MASKED_BIT_DISABLE(0xffff));
> + /* something from same cacheline, but !FORCEWAKE_VLV */
> + POSTING_READ(FORCEWAKE_ACK_VLV);
> }
>
> static void vlv_force_wake_get(struct drm_i915_private *dev_priv)
> @@ -4371,7 +4377,8 @@ static void vlv_force_wake_get(struct
> drm_i915_private *dev_priv)
> static void vlv_force_wake_put(struct drm_i915_private *dev_priv)
> {
> I915_WRITE_NOTRACE(FORCEWAKE_VLV,
> _MASKED_BIT_DISABLE(FORCEWAKE_KERNEL));
> - /* The below doubles as a POSTING_READ */
> + /* something from same cacheline, but !FORCEWAKE_VLV */
> + POSTING_READ(FORCEWAKE_ACK_VLV);
> gen6_gt_check_fifodbg(dev_priv);
> }
>
>
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